I. Field
The present invention relates generally to communication, and more specifically to techniques for determining coverage and switching between overlay communication systems.
II. Background
Wireless communication systems are widely deployed to provide various communication services such as voice, packet data, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources. Examples of such multiple-access systems include Code Division Multiple Access (CDMA) systems, Time Division Multiple Access (TDMA) systems, and Frequency Division Multiple Access (FDMA) systems. A CDMA system may implement a radio access technology (RAT) such as cdma2000, Wideband-CDMA (W-CDMA), and so on. cdma2000 covers IS-2000, IS-856, and IS-95 standards. A TDMA system may implement Global System for Mobile Communications (GSM) for over-the-air communication and General Packet Radio Service (GPRS) for packet data transmission. These various RATs and standards are known in the art.
Some wireless communication systems (e.g., cdma2000, W-CDMA, and GSM/GPRS systems) are capable of providing voice and packet data services. Each type of service has different characteristics. For example, voice service typically requires a common grade of service (GoS) for all users as well as relatively stringent delays. In contrast, packet data service may be able to tolerate different GoS for different users and may further be able to tolerate variable delays. To support both voice and packet data services, a wireless communication system may first allocate system resources to voice users and then allocate any remaining system resources to packet data users who are able to tolerate longer delays.
Some wireless communication systems are optimized for packet data transmission, which is typically characterized by long periods of silence punctuated by large bursts of traffic. One such system is an IS-856 system, which allocates most or all of the system resources to one user at any given time, thereby greatly increasing the peak data rate for the user being served.
A service provider/network operator may deploy multiple wireless communication systems to provide enhanced services for its subscribers. For example, a service provider may deploy one system capable of providing both voice and packet data services for a large geographic area and may deploy another system capable of providing packet data service for areas where packet data usage is expected to be high. The coverage areas of the two systems typically overlap, and these systems would be considered as “overlay” systems. A multi-mode/hybrid terminal may be able to receive service from one of the two systems at any given moment depending on the location of the terminal and the desired service. Some of the challenges in such overlay systems include (1) determining the coverage boundaries of the individual systems and (2) deciding when the terminal should switch between the two systems.
There is therefore a need in the art for techniques to determine coverage and to switch between overlay communication systems.